kWh calculator: power times time, battery energy and kWh per kWp

Three small tools: power times time, battery energy, and kWh per kWp. Use a decimal point and no thousands separator. Defaults are the page's invented example. A design aid, not a guarantee basis.

1. Power times time

Power

Power unit

Time at that power

Time unit

Energy: - kWh

- Wh, - MJ, - Btu

1 kWh = 3.6 MJ exactly (NIST SP 811) and 3,412 Btu (EIA). Constant power only; for a changing load, add up one row per period.

2. Battery: nominal, usable and delivered kWh

Nominal energy, kWh (sheet "energy" or "capacity")

Usable kWh from the sheet (or leave blank)

Usable share %, used only if usable kWh is blank

Discharge efficiency, %

Load to carry, kW

Battery power limit, kW (optional)

Usable energy: - kWh

Delivered at the output: - kWh

Runtime at the load: - hours

Runtime at the power limit: - hours

The 94% discharge efficiency is an invented placeholder. Ask the maker which side of the inverter its kWh figures are on.

Optional check: nominal voltage, V

Capacity, Ah

Volts x amp-hours: - kWh

3. kWh per kWp

Annual AC energy, kWh

Array size, kWp DC at STC

Specific yield: - kWh/kWp

Average per day: - kWh. Average power over 8,760 hours: - kW